Image receiving layer for the silver salt diffusion process

ABSTRACT

CONTINUOUS-TONE OR LINE IMAGES CAN BE PRODUCED BY THE SILVER SALT DIFFUSION PROCESS BY IMAGEWISE EXPOSING A SILVER HALIDE EMULSION LAYER TRANSFERRING THE SILVER HALIDE FROM THE UNEXPOSED POSITIONS TO AN IMAGE-RECEIVING LAYER AND REDUCING THE TRANSFERRED SILVER HALIDE TO SILVER. PARTICULARLY USEFUL FOR THE IMAGE-RECEIVING LAYER IS A WATER INSOLUBLE MIXTURE OF CELLULOSE ACETATE AND AN ACETAL OF POLYVINYL ALCOHOL WHICH IS PERMEABLE TO MOISTURE.

United States Patent O 3,690,885 IMAGE RECEIVING LAYER FOR THE SILVER SALT DIFFUSION PROCESS Werner Krafft, Leverkusen, Peter Kruck, Cologne, and

Rudolf Meyer and Maria Scheibitz, Leverkusen, Germany, assignors to Agfa-Gevaert Aktiengesellschaft, Leverkusen, Germany No Drawing. Filed Nov. 4, 1970, Ser. No. 86,943 Claims priority, application Germany, Nov. 6, 1969, P 19 55 899.7 Int. Cl. G03c 5/54 US. C]. 96-29 R 5 Claims ABSTRACT OF THE DISCLOSURE Continuous-tone or line images can be produced by the silver salt diffusion process by imagewise exposing a silver halide emulsion layer transferring the silver halide from the unexposed positions to an image-receiving layer and reducing the transferred silver halide to silver. Particularly useful for the image-receiving layer is a water insoluble mixture of cellulose acetate and an acetal of polyvinyl alcohol which is permeable to moisture.

The invention relates to image receiving layers which contain binder mixtures which are insoluble in water but which are suflicient capable of swelling in water and permeable to moisture, in particular for the production of line and continuous tone images by the silver salt diffusion process.

The usual water-soluble binding agents for image-receiving layers for the silver salt diffusion process such as gelatin, polyvinyl alcohol, carboxymethyl cellulose, alginic acid derivatives, etc. take up more liquid than is required for photographic processing. This gives rise to disadvantages such as increased take-up of developer liquid and hence greater risk of yellowing in the final images, reduced stability of the processed layers due to the greater take-up of moisture during storage at high humidity and increase in the length of time required for transfer of the silver halide from the light-sensitive layers to the imagereceiving layer due to the longer diffusion distance resulting from the increased swelling. Moreover, greater length of time is required for drying the swelled layers.

Special difficulties in this respect are encountered with image receiving layers for processes in which the positive continuous tone images are instantly obtained in the camera by silver salt diffusion. The known image receiving layers for this process generally contain a substantial proportion of colloidal silicic acid. They must be coated with a protective layer after processing in order to provide mechanical protection for the silver image which is deposited on the paper support and which is very easily scratched off. In addition, this protective coating contains other compounds for stabilizing the image and neutralizing the alkaline developer solution which remains in the layer.

Image receiving layers which no longer require this protective coating are also known. Such image receiving layers consist e.g. of a layer of a synthetic binder of the polyvinyl acetal or cellulose acetate type which contains nuclei and which has been saponified with acid or alkali before development in order to be permeable to alkali and hence capable of development. The finely divided noble metals used as development nuclei for these layers must be applied to the powdered binder by evaporation at elevated temperature or by glow discharge in a high vacuum. These image receiving layers are only of limited utility because the application of the nuclei by evaporation and the carefully controlled hydrolysis of the binding agent involve considerable difficulties.

It is among the objects of the invention to provide a binding agent or mixture of binding agents for the imagereceiving layer, in particular for the production of continuous tone images, which are practically insoluble in water and undergoes very little swelling but yet are sufficiently permeable to water and protect and stabilize the silver image produced in the layer.

We now have found an image-receiving material for the silver salt diffusion process comprising a supported layer containing development nuclei incorporated in a binding agent which consists of a mixture of a cellulose acetate having an acetic acid content of between 30 and 50% by weight and a mixed acetal of polyvinyl alcohol with a benzaldehyde and a sulfonated benzaldehyde. Preferred are mixed acetals which contain up to 40% by weight of free vinyl alcohol units.

Layers which contain the mixed acetal of polyvinyl alcohol in quantities of 40 to by weight, based on the cellulose acetate, have proved to be especially suitable.

The molar ratio of benzaldehyde to sulfonated benzaldehyde in the mixed acetal may vary between 0.5 and about 3; products which contain the two aldehyde components in a molar ratio of about 1:1 are preferred.

In particular suitable are mixed acetals of polyvinyl alcohol which contain 30 to 40% by weight of vinyl alcohol units being acetalized with benzaldehyde, 30 to 40% by weight of vinyl alcohol units being acetalized with sulfonated benzaldehyde and 20 to 40% by weight of free vinyl alcohol units. The mixed acetals should still be readily soluble in organic solvents but should only swell slightly in cold water.

The sulfonated benzaldehyde may contain one or more, preferably one or two sulfo groups. The benzene rings of the two aldehydes may contain further substituents, e.g. alkyl or alkoxy groups containing preferably one or two carbon atoms, or halogen such as chlorine or bromine, carboxyl and the like.

The usual development nuclei may be used for the image receiving material according to the invention, e.g. heavy metal sulfides or selenides such as silver sulfide, nickel sulfide, zinc sulfide or mixtures thereof, or heavy metals in a finely divided colloidal form, e.g. silver or palladium or mixtures thereof. The concentration of the nuclei in the image receiving layer can be varied with wide limits. Amounts of 3 to 15 mg. per square meter have generally been found suflicient. The optimum amount for each particular material can be determined by a few simple tests customarily employed in the art.

The image receiving material according to the invention is suitable for the processing of the usual light-sensitive materials used for the silver salt difiustion process. These are generally materials which contain one or more silver halide gelatin emulsion layers. Materials comprising silver halide emulsion layers in which the silver halide consists substantially of silver chloride are especially suitable. Suitable light-sensitive layers have been described e.g. in German Pat. No. 912,294 and in US. Pat. No. 2,603,565.

The preparation of suitable mixed acetals has been described in German Pats. Nos. 1,080,397 and 1,201,680. The polyvinyl alcohols used for this purpose may have a molecular weight of between 10,000 and 100,000. Polyvinyl alcohols having a molecular weight of between 20,000 and 50,000 are especially suitable.

The binding agent of image-receiving layers preferably consists substantially only of the mixture of cellulose acetate and mixed acetal.

The image receiving materials according to the invention may be processed in the usual manner together with the light-sensitive materials, e.g. using liquid proccssing baths, or they may be used for the production of continuous-tone images directly in the camera, using processing pastes. The materials according to the invention are especially suitable for the last-mentioned purpose.

Excellent smooth layers of high mechanical strength can be cast from the binder mixture used according to the invention. Sufficient scratch resistance is ensured even at high humidity. The use of the binding agents does not require any additional measures such as saponification or the use of a special protective coatings after processing. The scratch resistance is excellent and the permeability to water, although generally applied from an organic aqueous medium, is quite sufficient.

EXAMPLE 1 First layer.A first layer of mixed acetal having the following composition is applied to a baryta-coated paper support which has a weight of about 140 g./m. and which has been treated with a layer of cellulose triacetate:

100 ml. of mixed acetal solution, 3% in methanol, 150 ml. of methyl glycol, 100 ml. of acetone.

The mixed acetal consists of a mixture of 32 to 35% of benzaldehyde disulfonate vinyl alcohol units, 33 to 38% of benzaldehyde vinyl alcohol units and 27 to 33% of free vinyl alcohol units. The first layer serves to increase the absorption capacity of the nucleated layer applied on it and hence to improve the silver transfer.

Layer containing nuclei.-The following casting solution is applied to the layer described above:

55 ml. of cellulose acetate solution, acetic acid content 44% by weight, 3% in acetone/water 4:1,

170 ml. of acetone,

20 ml. of water,

75 ml. of methyl glycol,

30 ml. of a 3% methanolic solution of the aforesaid mixed acetal,

2 ml. of a concentrate of nuclei.

The concentrate of nuclei has the following composition:

100 ml. of an aqueous silicic acid sol (silicic acid content 30% by weight adjusted to pH 3 by means of ionic exchanger),

0.5 ml. of a 1 N Na Pd-Cl solution,

ml. of a 2% acetonic solution of l-phenyl pyrazolidone.

In order to prevent residues of developer paste adhering to the image receiving layer after the development, the layer which contains the nuclei is subsequently coated with a thin protective layer of carboxymethyl cellulose. This protective coating consists of a mixture of:

4 300 ml. of a 3% aqueous solution of carboxymethyl cellulose, 15 ml. of a 4% aqueous solution of nonylphenol polyglycol ether as wetting agent.

The three layers are applied to the paper support by the dip-coating method at the rate of 3 to 3.5 m./min. and dried in warm static air under mild conditions of drying, the guide rollers over which the web of paper is placed being heated to about 70 C.

Processing.-A silver halide gelatin emulsion layer on a support of baryta-coated paper is imagewise exposed. The exposed layer is brought into contact with the nucleated layer of the image-receiving material described above, and a developer of pasty consistency is applied between the two layers by the usual methods (see e.g. German Pat. No. 912,294 or US. Pat. No. 2,603,565). This developer has the following composition:

6.7 g. of carboxymethyl cellulose,

5.1 g. of Na SO sicc.

0.5 g. of p-methylaminophenol 5 g. of NaOH,

2 g. of N,N-allyl-oxyurea,

0.05 g. of Z-amino-S-mercapto-l-thia-3,4-diazole dissolved in water up to ml.

The reaction time is a few seconds. After separation of the two images, a positive, scratch-resistant silver image of the original is obtained which has high contrast and good reproduction of the continuous tones.

EXAMPLE 2 A paper support as described in Example 1 is coated with a nucleated layer from a casting solution of the following composition:

50 ml. of a cellulose acetate solution (acetic acid content 43% by weight, 3% solution in acetone/water 4:1)

ml. of acetone 18 ml. of water 75 ml. of methyl glycol 30 ml. of a mixed acetal of polyvinyl alcohol (3% by weight in methanol) 2.5 ml. of a 0.1 nAgNO aqueous solution,

2.0 ml. of a 0.1 in aqueous solution of sodium sulfide The mixed acetal contains 38% by weight of vinyl alcohol units being acetalised with benzaldehyde, 34% by weight of vinyl alcohol units being acetalised with disulfo-benzaldehyde and 28% by weight of free vinyl alcohol units.

Further processing is accomplished as described in Example 1.

We claim:

1. In an image receiving material which is adapted to receive the transfer of silver halide from silver halide light sensitive material, the combination of a support, and a layer on said support for receiving silver halide from unexposed portions of a silver halide light sensitive layer, said layer comprising a binding agent consisting of a mixture of a cellulose acetate having an acetic acid content of between 30 and 50% by weight and a mixed acetal of polyvinyl alcohol with benzaldehyde and sulfonated benzaldehyde in an amount of 40 to 60% by Weight, based on the cellulose acetate and finely divided metals or metal compounds which provided nuclei for development of the silver halide.

2. The image-receiving material of claim 1, wherein the binding agents contain 40 to 60% by weight of the mixed acetal of polyvinyl alcohol, based on the cellulose acetate.

5 6 3. The image-receiving material of claim 1 wherein References Cited ghfefilixegin 3.5232210 1cigiitains up to 40% by weight of units UNITED STATES PATENTS 4. The image-receiving material of claim 1, wherein 3,455,686 7/1969 Famey et 96-29 D the mixed acetal contains 30 to 40% by weight of vinyl 5 3,455,685 7/1969 Carlson et 96 29 D alcohol units being acetalised with benzaldehyde, 30 to 40% by weight of vinyl alcohol units being acetalised NORMAN TORCHIN Pnmary Exammer with sulfonated benzaldehyde and 20 to 40% by weight J. L. GOODROW, Assistant Examiner of free vinyl alcohol units.

5. The image-receiving material of claim 1, wherein 10 the mixed acetal contains benzaldehyde and sulfonated 9676 R benzaldehyde in the molar ratio of 1:05 to 2.5.

US. Cl. X.R. 

